1. Field of the Invention
This invention relates to a wave compression supercharger wherein the energy of the exhaust gas of an engine is used to compress air inducted into the engine. More particularly, the invention pertains to such a supercharger wherein three complete cycles of wave compression occur during a single rotor revolution.
2. Description of the Prior Art
Our invention comprises improvements in a wave compression supercharger of the kind that is described in a publication of The American Society of Mechanical Engineers, dated Sept. 18-22, 1977 entitled, "Performance and Sociability of Comprex Supercharged Diesel Engines".
A wave compression supercharger is a device for producing an exchange of energy between pressurized, hot exhaust gas of an internal combustion engine and air at atmospheric pressure. Within the supercharger the ambient air is compressed and the exhaust gas expanded.
A conventional wave compression supercharger includes a cylindrical rotor having radially directed vanes extending from its outer surface. Generally, stationary port plates are positioned at opposite ends of the rotor and have inlet openings formed through their thicknesses to allow exhaust gas and ambient air to flow into the rotor. Additional openings are provided in the port plates through which the expanded exhaust gas and compressed air flow from the rotor. The pressure exchange takes place within the rotor cells defined by the spaces between the rotor vanes. The process for compressing the ambient air begins when a rotor cell rotates into general alignment with the air inlet port thereby allowing ambient air to flow into and to fill the rotor cell. Rotation then brings the rotor cell into general alignment with the exhaust gas inlet port thus admitting into the cell a compression wave, which begins to travel along the rotor in the direction of the inlet air port. The compression wave travels along the rotor ahead of the engine exhaust gas and operates to compress the air in the rotor cell as it travels axially toward the air port plate. The rotor will have rotated out of communication with the air inlet port when the compression wave has begun to travel down the rotor length thereby sealing the air side of the rotor cell.
Immediately before the compression wave reaches the air side of the rotor, the cell rotates out of alignment with the exhaust gas inlet port. Next, the rotor brings the cell to the air outlet port thus allowing the compressed air to be pumped from the rotor due to the action of the compressed wave traveling to the air side of the rotor. The rotor then brings the cell out of communication with the air outlet port and for a brief period the rotor cell is closed at both ends. In a similar way, the exhaust gas is purged from the rotor cell after the pressure wave rebounds from the air port plate surface. The rotor cell rotates into alignment with the exhaust gas outlet port when the rebounding compression wave returns to the exhaust gas port plate. At the air side of the rotor, the cell is open to ambient air during the latter portion of the compression wave movement to the gas side so that a partial vacuum tending to resist movement of the returning compression wave is avoided.
For efficient operation, it is necessary that the compression wave reaches the air side of the cell precisely as the cell rotates out of alignment with the high pressure air exhaust port. This port must be sized and positioned carefully with respect to the rotor cell and the air inlet port so that the rotor brings the cell to the port when the air in the cell has been compressed to a sufficient pressure, but before the engine exhaust gas, located behind the compression wave, reaches the end of the cell.
In view of the timed sequence of events within a wave compression supercharger with respect to the rotor speed, the position and location of the gas and air inlet and outlet ports and of the advance and return of the pressure wave along the rotor length, it can be appreciated that the device will operate efficiently generally at only one speed. However, the engine of the vehicle that drives the rotor must operate over a wide range of speed. It is, therefore, desirable to expand the efficient operating range of the supercharger to a greater portion of the speed range of the engine.
Recognizing the need to expand the optimal speed range of a wave compression supercharger, air and gas port plates have been mounted for angular adjustment so that the location of the ports formed through their thicknesses can vary as the rotor speed varies. A supercharger of this kind has been described in U.S. patent application Ser. No. 99,245, filed Dec. 3, 1979. Superchargers having the general characteristics in operation as described herein have been disclosed in U.S. patent applications Ser. No. 90,948, filed Nov. 5, 1979 and Ser. No. 32,324, filed Apr. 23, 1979, all assigned to the assignee of the present patent application.
Conventional wave compression superchargers have two sets of ports formed in each air port plate and exhaust gas port plate. These sets of port are identically spaced around the circumference of the rotor and are sized so that the two inlet ports and the two outlet ports have respectively equal areas. Furthermore, the ports are spaced symmetrically around the rotor circumference. This disposition of the air inlet and exhaust port permits two complete suction and compression cycles within each rotor cell for every revolution of the rotor. A high frequency siren-like noise is an operating characteristic of a wave compression supercharger of this convention type. The noise is recognized to be a serious problem in automotive usage.
The spacing of the ports and the circumferential length over which they extend is conventionally selected to produce the most efficient operation of the supercharger at a particular engine speed. The engine speed corresponding to the sizing of the ports is the speed at which the supercharger is required to produce positive boost, usually at or near the engine idle speed.
Conventional wave compression superchargers have two compression cycles for each revolution of the rotor. The air port plate has two large inlet ports of equal size and two smaller outlet ports of equal size formed through its thickness. The ports are distributed about the central axis of the rotor and extend in the circumferential direction a predetermined portion of the total circumference. Each port extends radially a distance that corresponds generally to the radial depth of the rotor cells.
Each compression cycle has one associated air inlet port and one air outlet port; the inlet ports are disposed between the outlet ports. Therefore, each compression cycle occurs during one-half of each rotor revolution because the several ports are arranged around the rotor circumference symmetrically about the central axis of the rotor. The arcuate distance between the adjacent edges of the inlet and outlet ports is the same for each compression cycle.